Particulate emissions of gasoline engines will be newly regulated in Europe in 2014 with the introduction of EU6a regulations of 6×1012 particles/km and further reduced to 6×1011 particles/km with the introduction of EU6c in 2017. Similarly, United States regulations will impose similarly challenging standards with the introduction of LEVIII. Standards are assumed to be 10 mg/mi in 2014, 3 mg/mi in 2018 and 1 mg/mi in 2025. A major source of particulate emissions is known to be from a diffusion flame fed by fuel evaporating from the deposits on the fuel injector tip.
It is known that protruding the fuel injector further into the combustion chamber reduces the particulate emissions. Increasing injector tip protrusion raises injector tip temperature by exposing more injector tip surface area to hot combustion gases. This in turn enhances evaporation of any fuel remaining on the tip so there is no or little fuel remaining on the tip to be ignited when the flame front passes. The higher tip temperature also enhances oxidation of the deposits on the tip reducing the sponge-like surface of the deposits which hold the fuel.
Although a seemingly simple enhancement, increasing the injector tip protrusion in an existing engine and injector is neither simple nor inexpensive. If the injector is essentially unchanged, protrusion can only be increased by changing the design and machining of the cylinder head and the fuel rail. In a high volume scenario these are not simple, inexpensive changes. Similarly, making the injector longer instead of changing the engine components impacts highly automated component manufacturing, assembly and test equipment resulting in large tooling expenses, a non-standard product, and quality risks associated with tooling and component changeovers.
Thus, there is a need to increase the injector tip temperature to lower particulate emissions without impacting engine or injector machining and assembly tooling in any major way.